Unpaved roads as seed corridors

Roads are often seen as barriers to movement and dispersal.  However, not all roads are created equal, and new research suggests that some types of human developed roads can in fact be beneficial to species dispersal by acting as corridors.  Roads that are unpaved or rarely used, such as dirt roads, fire breaks or logging routes, may facilitate the dispersal of seeds by acting as “highways” for large seed dispersers.  In their new article, Alberto Suárez-Esteban and colleagues show that unpaved roads are often used by medium and large sized carnivores and ungulates as pathways for movement throughout their range.  These frugivorous animals, which in this study included wild boar, red deer, fallow deer, red fox, European badger and European rabbits, often leave fecal deposits along the routes that include the seeds of plants they’ve eaten along with a healthy dose of fertilizer.  These seeds end up being dispersed a much larger distance due to the presence of the road than they would have without it, and in a manner that promotes seed germination.

In looking at quantities of seed dispersed, the authors found that unpaved roads actually contained higher numbers of native plants seeds than the surrounding native scrubland.  They conclude that unpaved roads act to promote seed dispersal, which can ultimately lead to reforestation of linear corridors that were previously cleared.  While the benefits of these unpaved roads represent a balancing act between providing an open matrix for movement and limiting human perturbations such as traffic or hunting, removal of these unpaved roads for conservation purposes does not always represent the best strategy.  In some cases it may be better to leave unpaved roads that are rarely used to promote species persistence in a region.  As a result, through long-distance seed dispersal and other benefits, carnivores can act as gardeners by providing a diverse pool of seeds for revegetation in humanized landscapes.